'Avatar' rock name was mined from science

Near the beginning of director James Cameron's "Avatar," a greedy businessman itching to dig a mine on the planet Pandora utters a line that set some viewers to snicker.

"This is why we're here," he explains. "Unobtainium. Because this little gray rock sells for 20 million a kilo. No other reason. This is what pays for the party."

Unobtainium? Really, Mr. Cameron? You invented an entirely new language, imagined a planet full of creatures and plants, concocted a new religion and you couldn't come up with a better name than … unobtainium?

How, um, disappointingium.

But Cameron wasn't out of creative juice. He was being clever.

Unobtainium is a real concept in engineering and science, a jokey word used to describe a fantastical material that is either nearly impossible to get or simply doesn't exist. Similar terms include "handwavium," "rarium" and "wishalloy," as in: "If only I had some wishalloy, I could make this perpetual motion machine work!"

"Usually it has some unusual feature — being extraordinarily strong or having unusual electrical properties or being able to resist being deformed," said David Stevenson, professor of planetary science at California Institute of Technology in Pasadena, Calif.

Harvard physicist David Weitz, a materials specialist, said he wishes he had some unobtainium to replace window glass. The stuff would be as cheap and convenient as glass, but more efficient in controlling heat and light, he said.

"We are constantly coming up with these ideas," Weitz said. "In a certain sense, the role of scientists who work on materials is to know what is possible, what does not violate the laws of physics. Unlike James Cameron, we cannot break the laws of physics."